$9.$ The process of breaking down large hydrocarbon molecules into smaller ones is known as:

a$)$ Cracking

b$)$ Reforming

c$)$ Alkylation

d$)$ Polymerization

$10.$ Which of the following is a characteristic of diesel fuel?

a$)$ High octane rating

b$)$ Low viscosity

c$)$ High sulfur content

d$)$ Low cetane number

$11.$ The refining process that rearranges the molecular structure of hydrocarbons to increase their octane rating is called:

a$)$ Cracking

b$)$ Reforming

c$)$ Alkylation

d$)$ Isomerization

$12.$ Which refining process converts straight$-$chain hydrocarbons into branched$-$chain hydrocarbons?

a$)$ Cracking

b$)$ Reforming

c$)$ Alkylation

d$)$ Isomerization